Distributor Question

[hambone]

What happens when you try to run a type4 distributor on a type1 engine? I'd imagine the advance curve is wrong and the performance will suffer...
Also, why is there a different distributor specified for a 1971 Beetle VS Bus? It is the same engine...

BTW Anyone need a distributor for an early type4? 1970-72 914/412 with dual can.

[Xelmon]

Did a quick search on the interwebs... I wouldn't have guessed it just by sitting here, yet it makes sense.

Bus '71
Advance/Retard Range: Vacuum: 2-5deg Adv, 11-13deg Ret; Centrifugal: 12-16deg @ 2200rpm, 22-25deg @ 3800rpm

Bug '71
Advance/Retard Range: Vacuum: 9-12deg Adv, 11-13deg Ret; Centrifugal: 6-12deg @ 1500rpm, 22-25deg @ 3800rpm

It took way too long to remember why it works the way it does... Keep in mind people that I am operation under general engine characteristics.

Basically ignition takes a few things - engine vacuum, etc - to calculate the advance of the vehicle. It takes a lot of time to figure it out, the main take away is that the higher the load, the more advance you need, aka, you have more advance when you are at WOT.

Since the bus is heavier, it effectively increases the load on the engine, and thus the advance has to be restricted to increase the longevity of the engine, and thus the difference of ~17 degrees vs ~10 degrees of max advance.

Link of dizzies: http://www.oldvolkshome.com/ignition.htm#B1971

BTW, Colin, if I am spreading nothing but misinformation, correct me.

[kreemoweet]

The '71 bus and bug engines were attached to transmissions with very different gearing, and bodies with very different weights. The '71 bus and bug had the "same"
34 PICT-3 carburetor but the jetting and other specs were very different. Stands to reason the timing specs might also vary.

[hambone]

With a single port engine, having the correct distributor really helped with performance. But, in that era VW used the same distributor for Type I or 2. I seem to remember VW chasing their tail in the 70s trying to comply with emissions regulations, could this be a result of that?
What is exactly the point of 2 vacuum cans, and can you do without?

Thanks, trying to wrap my head around this, and how it affects us here in the modern age.

Maybe I should ask this: what is the best distributor for a '69 Bus with a dual port 1600? I'm guessing this one:
Bus & Pickup 1971 * 1600
Distributor: VW 211-905-205Q, Bosch 0231 167 055 or 211-905-205S, 0231 180 001 > 043-905-205D, 0231 176 033
113-905-205AH (which is for an autostick Bug, interesting....)

Yes good luck finding a 1-year part. Which leads me to this option, possibly not perfect for a bus but a hell of a lot better than a 009:
Beetle 1972-1973 * 1600 Manual Trans
Distributor: VW 113-905-205AN, Bosch 0231 167 070 > 043-905-205C, 0231 176 028
Can Use: VW 113-905-205AJ, Bosch 0231 167 049

And finally, the SVDA that everyone seems to rave about:
http://vwparts.aircooled.net/Pertronix- ... 186504.htm

Of course this also leads me to more persnickity: how does one create a "proper" 34pict3 for a bus? I don't really want to know...

[hambone]

FWIW I actually found a couple 205Q distributors out there, but they most likely need rebuilding. Is it worth the hassle getting the exact distributor?

[Xelmon]

I'd say most definitely yes, and do a rebuild.

Alternatively, figure out what changes between the dizzies and build a mutant dizzy.

Never the less, in my mind you'd have to tune the engine to max advance at cruising RPM, so that means that you'd have to retard the curve ~7 degrees.
Doing that you'll have ~2 degree BTDC idle, which could get a bit rough. Hell, I know of my GMC that 4 degrees here or there makes a very big difference. Since your advance curve would be wonky, so would also lose a bit of power.

[hambone]

According to OVH here is the timing spec, it is at idle:

Timing Set At:: 5deg ATDC @ 800-950rpm w/strobe, vacuum hose(s) connected

Full-advance should match that at 30 deg. BTDC I imagine...
Let me get some cabbage together and get this straightened out.

[hambone]

Thanks Adam that really did help. What does it mean to "retard the curve"? Isn't the advance curve based on the HP peak? If you "move the curve to the left" so to speak, doesn't it affect peak power?
Can any early Bay guys chime in? At this point I think my practical question is whether to go with the stock '71 Q distributor, or the new, possibly Chinese Pertronix SVDA (The AC NET one is NLA, BTW).

You know the frustrating thing is, once you learn all this stuff it's already 25 years obsolete at least! Old arts. And then our synapses fade away too....

[hambone]

I would also like to ask again:
"What is exactly the point of 2 vacuum cans, and can you do without?"

[ruckman101]

I chased the "Q" distributor for quite some time, including the exactly perfect vacuum can (how much? Ouch!) before I bailed and invested in the Air-cooled.net SVDA. You're welcome to go through my distributor graveyard drawer l've got up here that are what's left of my efforts. None of them had two vacuum cans, though some had push/pull vacuum cans. Somehow a 258 vacuum can rings a bell.

neal

[Amskeptic]

the higher the load, the more advance you need, aka, you have more advance when you are at WOT.

So very not correct, I am sorry. The higher the load, the more air is in the cylinders, and the quicker it is to detonate. As the load increases, the *vacuum advance* is taken out and the default value of the centrifugal curve is our ceiling. It is only speed sensitive, and is determined primarily by volumetric efficiency.

Since the bus is heavier, the advance has to be restricted to decrease heat load engine,

and thus the difference of ~17 degrees vs ~10 degrees of max advance.
Colin, if I am spreading nothing but misinformation, correct me.

Indeed . . . look at the total advance, and you will see identical numbers at full throttle (*i.e. no vacuum, just centrifugal), this reflects the actual mechanical limits of this engine design.

In the details of different applications, bugs use more vacuum advance moderation as part of the whole timing map, and the bus relies more on the centrifugal map because, as you stated sort-of, the accelerator pedal spends far more time on the floor.
Colin

[Amskeptic]

I would also like to ask again:
"What is exactly the point of 2 vacuum cans, and can you do without?"

Retard is used for 34 Pict3 air bypass carburetors so they cram more air through the engine whilst maintaining a normal engine idle speed. The timing is retarded to make the engine weak so all that air only ends up running a 900 rpm or so. This was a brilliant way to dilute the idle air to pass emissions.

Never time a retard-equipped engine at idle without knowing first that the retard unit is actually functional, otherwise, if you time it at 5*ATDC. you will retard the whole timing map and end up with a hot exhaust and a doggy anemic engine. I say, pull the hoses, and time to 28* @ 3,200-3,400 rpm.
Colin

[hambone]

A valuable paragraph, thank you. So many grains of rice...

[Xelmon]

So very not correct, I am sorry. The higher the load, the more air is in the cylinders, and the quicker it is to detonate. As the load increases, the *vacuum advance* is taken out and the default value of the centrifugal curve is our ceiling. It is only speed sensitive, and is determined primarily by volumetric efficiency.

Ooook, so I did have it backwards and completely forgot about transitional/continuous situations. Hm, writing technical responses just after work finished may not be so wise. XD

Indeed . . . look at the total advance, and you will see identical numbers at full throttle (*i.e. no vacuum, just centrifugal), this reflects the actual mechanical limits of this engine design.

In the details of different applications, bugs use more vacuum advance moderation as part of the whole timing map, and the bus relies more on the centrifugal map because, as you stated sort-of, the accelerator pedal spends far more time on the floor.
Colin

Aaaaaa, that explains it! I was wondering when the advance kicked on-and-off.
Sweet, the race-car stuff really paid off in understanding this stuff!